U.S. patent application number 13/686186 was filed with the patent office on 2013-06-27 for support, lithographic apparatus and device manufacturing method.
This patent application is currently assigned to ASML Netherlands B.V.. The applicant listed for this patent is ASML Netherlands B.V.. Invention is credited to Theodorus Petrus Maria CADEE, Harmeet SINGH, Koen Jacobus Johannes Maria ZAAL.
Application Number | 20130164688 13/686186 |
Document ID | / |
Family ID | 48654892 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130164688 |
Kind Code |
A1 |
CADEE; Theodorus Petrus Maria ;
et al. |
June 27, 2013 |
Support, Lithographic Apparatus and Device Manufacturing Method
Abstract
A support for an object, e.g., a semiconductor substrate,
includes a main body having a surface configured and arranged to
have a plurality of projections. Each of the projections has an
associated electrostatic actuator for displacing a free end of the
associated projection relative to the main body at least in a
direction in a plane parallel to a main surface of the object.
Inventors: |
CADEE; Theodorus Petrus Maria;
(Asten, NL) ; ZAAL; Koen Jacobus Johannes Maria;
(Eindhoven, NL) ; SINGH; Harmeet; (Fremont,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASML Netherlands B.V.; |
Veldhoven |
|
NL |
|
|
Assignee: |
ASML Netherlands B.V.
Veldhoven
NL
|
Family ID: |
48654892 |
Appl. No.: |
13/686186 |
Filed: |
November 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61579931 |
Dec 23, 2011 |
|
|
|
Current U.S.
Class: |
430/322 ; 269/58;
355/72 |
Current CPC
Class: |
G03F 7/2051 20130101;
G03F 7/70708 20130101; G03F 7/707 20130101; H01L 21/683 20130101;
G03B 27/58 20130101 |
Class at
Publication: |
430/322 ; 355/72;
269/58 |
International
Class: |
G03B 27/58 20060101
G03B027/58; G03F 7/20 20060101 G03F007/20; H01L 21/683 20060101
H01L021/683 |
Claims
1. A lithographic apparatus comprising: a support for supporting an
object, wherein: the support comprises a plurality of projections
projecting from a surface of a main body; each respective one of
the projections includes at least one respective electrostatic
actuator configured to displace a respective free end of the
respective projection relative to the main body; and the respective
free end of the respective projection is displaceable by the
respective electrostatic actuator in a direction with a component
in a plane parallel to the surface of the main body from which the
projections project.
2. The lithographic apparatus of claim 1, wherein each respective
one of the projections has a further plurality of respective
electrostatic actuators.
3. The lithographic apparatus of claim 2, wherein the further
plurality of respective electrostatic actuators are distributed
around an axis of the respective projection.
4. The lithographic apparatus of claim 1, wherein: each respective
one of the projections has a first respective electrostatic
actuator, a second respective electrostatic actuator and a third
respective electrostatic actuator; the first respective
electrostatic actuator has a first center; the second respective
electrostatic actuator has a second center; the third respective
electrostatic actuator has a third center; and the first center,
the second center and the third center are radially separated, in a
further plane parallel to the surface of the main body, by
substantially 120.degree..
5. The lithographic apparatus of claim 1, wherein each respective
one of the projections further comprises an isolating electrode for
isolating the object on the support from electric fields generated
by the respective electrostatic actuator.
6. The lithographic apparatus of claim 1, further comprising a
controller that is operative to control applying a respective
electric charge to the respective electrostatic actuator under
control of a spatial variation in flatness of a top surface of the
object.
7. A support for supporting an object, comprising: a plurality of
projections projecting from a surface of a main body; each
respective one of the projections including at least one respective
electrostatic actuator configured to displace a respective free end
of the respective projection relative to the main body; and the
respective free end of the respective projection being displaceable
by the respective electrostatic actuator in a direction with a
component in a plane parallel to the surface of the main body from
which the projections project.
8. The support of claim 7, wherein each respective one of the
projections has a further plurality of respective electrostatic
actuators.
9. The support of claim 8, wherein the further plurality of
respective electrostatic actuators are distributed around an axis
of the respective projection.
10. The support of claim 7, wherein: each respective one of the
projections has a first respective electrostatic actuator, a second
respective electrostatic actuator and a third respective
electrostatic actuator; the first respective electrostatic actuator
has a first center; the second respective electrostatic actuator
has a second center; the third respective electrostatic actuator
has a third center; and the first center, the second center and the
third center are radially separated, in a further plane parallel to
the surface of the main body, by substantially 120.degree..
11. The support of claim 7, wherein each respective one of the
projections further comprises an isolating electrode configured to
isolate the object on the support from electric fields generated by
the respective electrostatic actuator.
12. A device manufacturing method comprising: projecting a
radiation beam onto a top surface of a substrate supported on free
ends of a plurality of projections from a surface of a main body of
a substrate support; and changing a profile of the top surface of
the substrate by displacing the free end of at least one of the
projections relative to the main body using an electrostatic
actuator associated with the projection.
Description
BACKGROUND
[0001] 1. Field of Invention
[0002] The present invention relates to a support, a lithographic
apparatus and a device manufacturing method.
[0003] 2. Related Art
[0004] A lithographic apparatus is a machine that applies a desired
pattern onto a substrate, usually onto a target portion of the
substrate. A lithographic apparatus can be used, for example, in
the manufacture of integrated circuits (ICs). In that instance, a
patterning device, which is alternatively referred to as a mask or
a reticle, may be used to generate a circuit pattern to be formed
on an individual layer of the IC. This pattern can be transferred
onto a target portion (e.g., comprising part of, one, or several
dies) on a substrate (e.g., a silicon wafer). Transfer of the
pattern is typically via imaging onto a layer of
radiation-sensitive material (resist) provided on the substrate. In
general, a single substrate will contain a network of adjacent
target portions that are successively patterned. Known lithographic
apparatus include so-called steppers, in which each target portion
is irradiated by exposing an entire pattern onto the target portion
at one time, and so-called scanners, in which each target portion
is irradiated by scanning the pattern through a radiation beam in a
given direction (the "scanning"-direction) while synchronously
scanning the substrate parallel or anti-parallel to this direction.
It is also possible to transfer the pattern from the patterning
device to the substrate by imprinting the pattern onto the
substrate.
[0005] The machine may be one in which a liquid having a relatively
high refractive index, e.g., water, fills a space between the final
element of the projection system and the substrate. In an
embodiment, the liquid is distilled water, although another liquid
can be used. Another fluid may be suitable, particularly a wetting
fluid, an incompressible fluid and/or a fluid with higher
refractive index than air, desirably a higher refractive index than
water. Fluids excluding gases are particularly desirable. The point
of this is to enable imaging of smaller features since the exposure
radiation will have a shorter wavelength in the liquid. (The effect
of the liquid may also be regarded as increasing the effective
numerical aperture (NA) of the system and also increasing the depth
of focus.) Other immersion liquids have been proposed, including
water with solid particles (e.g., quartz) suspended therein, or a
liquid with a nano-particle suspension (e.g., particles with a
maximum dimension of up to 10 nm). The suspended particles may or
may not have a similar or the same refractive index as the liquid
in which they are suspended. Other liquids which may be suitable
include a hydrocarbon, such as an aromatic, a fluorohydrocarbon,
and/or an aqueous solution.
[0006] Instead of a circuit pattern, the patterning device may be
used to generate other patterns, for example a color filter
pattern, or a matrix of dots. Instead of a conventional mask, the
patterning device may comprise a patterning array that comprises an
array of individually controllable elements that generate the
circuit or other applicable pattern. An advantage of such a
"maskless" system compared to a conventional mask-based system is
that the pattern can be provided and/or changed more quickly and
for less cost.
[0007] Thus, a maskless system includes a programmable patterning
device (e.g., a spatial light modulator, a contrast device, etc.).
The programmable patterning device is programmed (e.g.,
electronically or optically) to form the desired patterned beam
using the array of individually controllable elements. Types of
programmable patterning devices include micro-mirror arrays, liquid
crystal display (LCD) arrays, grating light valve arrays, and the
like.
[0008] The lithographic apparatus may be an EUV apparatus which
uses extreme ultra violet light (e.g., having a wavelength of 5-20
nm).
SUMMARY
[0009] It is desirable to provide a support in which measures are
taken to improve the flatness of an object, e.g., a substrate, on
the support.
[0010] According to an aspect of the present invention, there is
provided a support for an object comprising: a plurality of
projections projecting from a surface of a main body; each of the
projections having an associated electrostatic actuator for
displacing a free end of the associated projection relative to the
main body.
[0011] According to an aspect of the present invention, there is
provided a device manufacturing method comprising projecting a
radiation beam onto a top surface of a substrate supported on free
ends of a plurality of projections from a surface of a main body of
a substrate support, wherein the profile of the top surface of the
substrate is changed by displacing the free end of at least one of
the projections relative to the main body using an electrostatic
actuator associated with the projection.
[0012] Further features and advantages of the invention, as well as
the structure and operation of various embodiments of the
invention, are described in detail below with reference to the
accompanying drawings. It is noted that the invention is not
limited to the specific embodiments described herein. Such
embodiments are presented herein for illustrative purposes only.
Additional embodiments will be apparent to persons skilled in the
relevant art(s) based on the teachings contained herein.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0013] The accompanying drawings, which are incorporated herein and
form part of the specification, illustrate the present invention
and, together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
relevant art(s) to make and use the invention.
[0014] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention.
[0015] FIG. 2 illustrates schematically and in plan a support
according to an embodiment.
[0016] FIG. 3 illustrates a cross-section through line III of FIG.
2.
[0017] FIG. 4 illustrates, in cross-section, a detail of an
actuator and associated projection.
[0018] FIG. 5 illustrates, in cross-section, a detail of an
actuator and associated projection.
[0019] FIG. 6 illustrates, in cross-section, a detail of a
projection with a plurality of associated actuators.
[0020] FIG. 7 illustrates, in plan, the embodiment of FIG. 6.
[0021] FIG. 8 illustrates, in plan, an embodiment of a projection
with multiple associated actuators.
[0022] FIG. 9 illustrates schematically and in plan a connection
scheme.
[0023] The features and advantages of the present invention will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings, in which like
reference characters identify corresponding elements throughout. In
the drawings, like reference numbers generally indicate identical,
functionally similar, and/or structurally similar elements. The
drawing in which an element first appears is indicated by the
leftmost digit(s) in the corresponding reference number.
DETAILED DESCRIPTION
[0024] This specification discloses one or more embodiments that
incorporate the features of this invention. The disclosed
embodiment(s) merely exemplify the invention. The scope of the
invention is not limited to the disclosed embodiment(s). The
invention is defined by the claims appended hereto.
[0025] The embodiment(s) described, and references in the
specification to "one embodiment", "an embodiment", "an example
embodiment", etc., indicate that the embodiment(s) described may
include a particular feature, structure, or characteristic, but
every embodiment may not necessarily include the particular
feature, structure, or characteristic. Moreover, such phrases are
not necessarily referring to the same embodiment. Further, when a
particular feature, structure, or characteristic is described in
connection with an embodiment, it is understood that it is within
the knowledge of one skilled in the art to effect such feature,
structure, or characteristic in connection with other embodiments
whether or not explicitly described.
[0026] Embodiments of the invention may be implemented in hardware,
firmware, software, or any combination thereof. Embodiments of the
invention may also be implemented as instructions stored on a
machine-readable medium, which may be read and executed by one or
more processors. A machine-readable medium may include any
mechanism for storing or transmitting information in a form
readable by a machine (e.g., a computing device). For example, a
machine-readable medium may include read only memory (ROM); random
access memory (RAM); magnetic disk storage media; optical storage
media; flash memory devices; electrical, optical, acoustical or
other forms of propagated signals (e.g., carrier waves, infrared
signals, digital signals, etc.), and others. Further, firmware,
software, routines, instructions may be described herein as
performing certain actions. However, it should be appreciated that
such descriptions are merely for convenience and that such actions
in fact result from computing devices, processors, controllers, or
other devices executing the firmware, software, routines,
instructions, etc.
[0027] As disclosed in WO 2010/032224, hereby incorporated in its
entirety by reference, instead of a conventional mask a modulator
may be configured to expose an exposure area of the substrate to a
plurality of beams modulated according to a desired pattern. The
projection system may be configured to project the modulated beams
onto the substrate and may comprise an array of lenses to receive
the plurality of beams. The projection system may be configured to
move the array of lenses with respect to the modulator during
exposure of the exposure area.
[0028] Substrates with increasing sizes are to be handled in a
lithographic apparatus. Presently substrate sizes up to 300 mm are
used in lithographic processes. It is desirable to increase
substrate diameters, for example to a diameter of approximately 450
mm. These larger substrates will have a smaller thickness to
diameter ratio, resulting in a reduced bending stiffness. As a
result, the substrates will have a larger gravitational deflection
on the three e-pins in the extended position, which could
inherently lead to larger substrate load grid errors and
potentially also overlay errors. Also the e-pins would need to have
a larger surface area to support the increased weight of the
substrate compared to a 300 mm diameter substrate and this can lead
to a decrease in flatness when the substrate is clamped to the
support (because in that state the substrate is not supported above
the e-pins).
[0029] With an increase in the substrate area, unless a substrate
table WT and substrate stage is made thinner, the depth of the
substrate table WT is increased in the same proportion as the width
and the length of the substrate table WT, and thus the diameter of
the substrate. Thus, although, for example for a 450 mm substrate W
relative to a 300 m substrate, the diameter increases
proportionately by 50%, the area of the substrate W and substrate
table WT each increases by 125 percent and the volume and mass of
the substrate table WT would increase by almost 240%. Such an
increase in volume is highly undesirable. However, in having a
thinner substrate table WT, the table is less stiff, more flexible
and susceptible to bending. Consequently, accurate positioning of
the substrate table WT and the substrate W it is supporting is more
difficult. A measure is required to enable such a more flexible
substrate table WT to be used effectively, i.e., its position to be
sufficiently accurately known.
[0030] A flat top surface of a substrate table can only be achieved
at high cost. In addition, during use, the flatness of a substrate
table can decrease. For example, this can be due to wear of the
surface which supports the substrate or due to contaminant
particles on the surface. Any unflatness of the support surface of
the substrate table will lead to unflatness of the top surface of
the substrate which is being supported on the support surface. This
is a problem with all sizes of substrate but is expected to be more
severe for substrates with a diameter of 450 mm compared to those
with a diameter of 300 mm.
[0031] Unflatness of the top surface of the substrate can be dealt
with by performing rotations in the X and Y directions (the
directions orthogonal to the optical axis of the projection system)
during exposure of the substrate. However, this is complex control
wise and can lead to a reduction in throughput and/or can
deleteriously introduce dynamic disturbances resulting in non
optimal overlay and focus control.
[0032] In U.S. Pat. No. 4,504,045, which is incorporated by
reference herein in its entirety, the use of piezoelectric
actuators in a top surface of a substrate table has been proposed.
However, it can be difficult to control the position of
piezoelectric actuators over even short periods of time.
[0033] Before describing such embodiments in more detail, however,
it is instructive to present an example environment in which
embodiments of the present invention may be implemented.
[0034] FIG. 1 schematically shows a lithographic apparatus LAP
including a source collector module SO according to an embodiment
of the invention. The apparatus comprises: an illumination system
(illuminator) IL configured to condition a radiation beam B (e.g.,
EUV radiation); a support structure (e.g., a mask table) MT
constructed to support a patterning device (e.g., a mask or a
reticle) MA and connected to a first positioner PM configured to
accurately position the patterning device; a substrate table (e.g.,
a wafer table) WT constructed to hold a substrate (e.g., a
resist-coated wafer) W and connected to a second positioner PW
configured to accurately position the substrate; and a projection
system (e.g., a reflective projection system) PS configured to
project a pattern imparted to the radiation beam B by patterning
device MA onto a target portion C (e.g., comprising one or more
dies) of the substrate W.
[0035] The illumination system may include various types of optical
components, such as refractive, reflective, catadioptric, magnetic,
electromagnetic, electrostatic or other types of optical
components, or any combination thereof, for directing, shaping, or
controlling radiation.
[0036] The support structure supports, i.e., bears the weight of,
the patterning device. It holds the patterning device in a manner
that depends on the orientation of the patterning device, the
design of the lithographic apparatus, and other conditions, such as
for example whether or not the patterning device is held in a
vacuum environment. The support structure can use mechanical,
vacuum, electrostatic or other clamping techniques to hold the
patterning device. The support structure may be a frame or a table,
for example, which may be fixed or movable as required. The support
structure may ensure that the patterning device is at a desired
position, for example with respect to the projection system. Any
use of the terms "reticle" or "mask" herein may be considered
synonymous with the more general term "patterning device."
[0037] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
radiation beam with a pattern in its cross-section such as to
create a pattern in a target portion of the substrate. It should be
noted that the pattern imparted to the radiation beam may not
exactly correspond to the desired pattern in the target portion of
the substrate, for example if the pattern includes phase-shifting
features or so called assist features. Generally, the pattern
imparted to the radiation beam will correspond to a particular
functional layer in a device being created in the target portion,
such as an integrated circuit.
[0038] The patterning device may be transmissive or reflective.
Examples of patterning devices include masks, programmable mirror
arrays, and programmable LCD panels. Masks are well known in
lithography, and include mask types such as binary, alternating
phase-shift, and attenuated phase-shift, as well as various hybrid
mask types. An example of a programmable mirror array employs a
matrix arrangement of small mirrors, each of which can be
individually tilted so as to reflect an incoming radiation beam in
different directions. The tilted mirrors impart a pattern in a
radiation beam which is reflected by the mirror matrix.
[0039] The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical systems, or any
combination thereof, as appropriate for the exposure radiation
being used, or for other factors such as the use of an immersion
liquid or the use of a vacuum. Any use of the term "projection
lens" herein may be considered as synonymous with the more general
term "projection system".
[0040] As here depicted, the apparatus is of a transmissive type
(e.g., employing a transmissive mask). Alternatively, the apparatus
may be of a reflective type (e.g., employing a programmable mirror
array of a type as referred to above, or employing a reflective
mask).
[0041] The lithographic apparatus may be of a type having two or
more tables (or stages or supports), e.g., two or more substrate
tables or a combination of one or more substrate tables and one or
more sensor or measurement tables. In such "multiple stage"
machines the additional tables may be used in parallel, or
preparatory steps may be carried out on one or more tables while
one or more other tables are being used for exposure. The
lithographic apparatus may have two or more patterning devices (or
stages or supports) which may be used in parallel in a similar
manner to substrate, sensor and measurement tables.
[0042] The lithographic apparatus may also be of a type wherein at
least a portion of the substrate may be covered by a liquid having
a relatively high refractive index, e.g., water, so as to fill a
space between the projection system and the substrate. An immersion
liquid may also be applied to other spaces in the lithographic
apparatus, for example, between the mask and the projection system.
Immersion techniques are well known in the art for increasing the
numerical aperture of projection systems. The term "immersion" as
used herein does not exclusively mean that a structure, such as a
substrate, must be submerged in liquid, but rather that liquid can
be located between the projection system and the substrate and/or
mask during exposure. This may or may not involve a structure, such
as a substrate, being submerged in liquid. Reference sign IM shows
where apparatus for implementing an immersion technique may be
located. Such apparatus may include a supply system for the
immersion liquid and a seal member for containing the liquid in the
region of interest. Such apparatus may optionally be arranged so
that the substrate table is fully covered by the immersion
liquid.
[0043] Illuminator IL receives a radiation beam from a radiation
source SO. The source and the lithographic apparatus may be
separate entities, for example when the source is an excimer laser.
In such cases, the source is not considered to form part of the
lithographic apparatus and the radiation beam is passed from the
source SO to the illuminator IL with the aid of a beam delivery
system BD comprising, for example, suitable directing mirrors
and/or a beam expander. In other cases the source may be an
integral part of the lithographic apparatus, for example when the
source is a mercury lamp. The source SO and the illuminator IL,
together with the beam delivery system BD if required, may be
referred to as a radiation system.
[0044] The illuminator IL may comprise an adjuster AD for adjusting
the angular intensity distribution of the radiation beam.
Generally, at least the outer and/or inner radial extent (commonly
referred to as .sigma.-outer and .sigma.-inner, respectively) of
the intensity distribution in a pupil plane of the illuminator can
be adjusted. In addition, the illuminator IL may comprise various
other components, such as an integrator IN and a condenser CO. The
illuminator may be used to condition the radiation beam, to have a
desired uniformity and intensity distribution in its cross-section.
Similar to the source SO, the illuminator IL may or may not be
considered to form part of the lithographic apparatus. For example,
the illuminator IL may be an integral part of the lithographic
apparatus or may be a separate entity from the lithographic
apparatus. In the latter case, the lithographic apparatus may be
configured to allow the illuminator IL to be mounted thereon.
Optionally, the illuminator IL is detachable and may be separately
provided (for example, by the lithographic apparatus manufacturer
or another supplier).
[0045] The radiation beam B is incident on the patterning device
(e.g., mask MA), which is held on the support structure (e.g., mask
table MT), and is patterned by the patterning device. Having
traversed the mask MA, the radiation beam B passes through the
projection system PS, which focuses the beam onto a target portion
C of the substrate W. With the aid of the second positioner PW and
position sensor IF (e.g., an interferometric device, linear encoder
or capacitive sensor), the substrate table WT can be moved
accurately, e.g., so as to position different target portions C in
the path of the radiation beam B. Similarly, the first positioner
PM and another position sensor (which is not explicitly depicted in
FIG. 1) can be used to accurately position the mask MA with respect
to the path of the radiation beam B, e.g., after mechanical
retrieval from a mask library, or during a scan. In general,
movement of the mask table MT may be realized with the aid of a
long-stroke module (coarse positioning) and a short-stroke module
(fine positioning), which form part of the first positioner PM.
Similarly, movement of the substrate table WT may be realized using
a long-stroke module and a short-stroke module, which form part of
the second positioner PW. In the case of a stepper (as opposed to a
scanner) the mask table MT may be connected to a short-stroke
actuator only, or may be fixed. Mask MA and substrate W may be
aligned using mask alignment marks M1, M2 and substrate alignment
marks P1, P2. Although the substrate alignment marks as illustrated
occupy dedicated target portions, they may be located in spaces
between target portions (these are known as scribe-lane alignment
marks). Similarly, in situations in which more than one die is
provided on the mask MA, the mask alignment marks may be located
between the dies.
[0046] The depicted apparatus could be used in at least one of the
following modes:
[0047] 1. In step mode, the mask table MT and the substrate table
WT are kept essentially stationary, while an entire pattern
imparted to the radiation beam is projected onto a target portion C
at one time (i.e., a single static exposure). The substrate table
WT is then shifted in the X and/or Y direction so that a different
target portion C can be exposed. In step mode, the maximum size of
the exposure field limits the size of the target portion C imaged
in a single static exposure.
[0048] 2. In scan mode, the mask table MT and the substrate table
WT are scanned synchronously while a pattern imparted to the
radiation beam is projected onto a target portion C (i.e., a single
dynamic exposure). The velocity and direction of the substrate
table WT relative to the mask table MT may be determined by the
(de-)magnification and image reversal characteristics of the
projection system PS. In scan mode, the maximum size of the
exposure field limits the width (in the non-scanning direction) of
the target portion in a single dynamic exposure, whereas the length
of the scanning motion partly determines the height (in the
scanning direction) of the target portion.
[0049] 3. In another mode, the mask table MT is kept essentially
stationary holding a programmable patterning device, and the
substrate table WT is moved or scanned while a pattern imparted to
the radiation beam is projected onto a target portion C. In this
mode, as in other modes, generally a pulsed radiation source is
employed and the programmable patterning device is updated as
required after each movement of the substrate table WT or in
between successive radiation pulses during a scan. This mode of
operation can be readily applied to maskless lithography that
utilizes a programmable patterning device, such as a programmable
mirror array of a type as referred to above.
[0050] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0051] The lithographic apparatus comprises a substrate table WT.
An upper part of the substrate table WT is shown in more detail in
FIGS. 2-8. FIG. 2 is a plan view of an embodiment of a support 1 of
a substrate table WT. The support 1 is configured to support an
object, in the case of a lithographic apparatus a substrate W.
[0052] The support 1 comprises a support surface 20. The support
surface 20 is configured to support the substrate W on the
substrate table WT. The support surface 20 is defined by a quantity
of discrete burls (projections 50, shown as black dots in FIG. 2)
which extend from a top surface 25 of a main body 22 to a
supporting height.
[0053] Projections 50 may have a pitch of about 1.5-3.0 mm, for
example. In an embodiment there are at least 40,000 projections
which form the support surface 20. In an embodiment there may be up
to 60,000 burls forming the support surface 20, or more. The top
surface of the projections 50 on which the substrate W is supported
defines the support surface 20.
[0054] The projections 50 are present in order to reduce the
surface area in contact with the substrate W when the substrate W
is placed on the substrate table WT. Each point of contact is a
source of potential contamination; reducing the total contact area
reduces the chance of contamination.
[0055] The support 1 is configured to receive the substrate W at a
pre-defined area on the support surface 20. The pre-defined area
comprises a center 30. The center 30 will receive the center of the
substrate W to be placed on the substrate table WT.
[0056] The pre-defined area may be designed to receive a substrate
W of relatively large size, for example a circular substrate of 450
mm in diameter. Such a large sized substrate W will have a small
thickness to diameter ratio, resulting in a reduced bending
stiffness. In an embodiment the pre-defined area may be designed to
receive a substrate W of a different shape, in plan and/or of a
different size to a circular substrate of 450 mm diameter.
[0057] FIG. 3 is a cross-section through the embodiment of FIG. 2
through line III marked on FIG. 2. FIG. 3 shows the plurality of
projections 50 which at their free end have a surface which forms
the support surface 20 and on which the substrate W is
supported.
[0058] Illustrated in dashed lines is the position of the substrate
W and of a projection 50a just after the substrate W has been
placed on the support 1. An area of unflatness 45 (a projection) is
present. Without adjustment, in order to avoid focus and/or overlay
errors during imaging rotation about the X and/or Y axis during
scanning is required. By adjusting the position of the projection
50a under the area of unflatness 45 in the Z-direction (downwards)
the flatness of the top surface of the substrate W (shown in solid
lines) can be improved. This results in there being less need for
rotations in the Rx and Ry directions during imaging and/or in
reduced overlay and/or focus errors.
[0059] The support 1 may be any sort of support 1. It may be a
support 1 which works on generating an underpressure between the
bottom of the substrate W, projections 50 and top surface 25 of the
main body 22. In an alternative embodiment the support 1 may be an
electrostatic support 1 in which the substrate W is attracted to
the support 1 by means of an electrostatic force. Electrostatic
force is generated by applying a potential difference between an
electrode of the support 1 and the substrate W (which may need a
conducting coating applied to its bottom surface for this
purpose).
[0060] The way in which the projection 50a may have its free end
which forms part of the support surface 20 displaced relative to
the main body 22 will be described with reference to FIGS. 4-8. In
an embodiment each of the projections 50 have an associated
electrostatic actuator 70 for displacing the free end of the
projection 50 associated with the electrostatic actuator 70
relative to the main body 25. In this way the shape of the support
surface 20 can be changed.
[0061] The advantage of an electrostatic actuator 70 over, for
example a piezoelectric actuator is that the displacement of such
an electrostatic actuator 70 is constant for a given potential
difference across electrodes of the electrostatic actuator 70.
Therefore, such a system is stable over time and drift in position
between setting of the position of the electrostatic actuator 70
and imaging is unlikely to occur or only to be small. This is
because an electrostatic actuator 70 maintains the charge applied
to it in the electrodes (electrically conductive layers 72, 74) and
it is this potential difference across a gap 76 (either occupied by
a vacuum, a gas or mixture of gases or a dielectric material
between electrodes (electrically conductive layers 72, 74), which
results in the displacement. Therefore, there is no leaking of the
charge from the electrodes (electrically conductive layers 72, 74)
because the charge is not distributed into the gap 76. This
contrasts with piezoelectric actuators where the charges are
distributed into the material of the piezoelectric actuator which
can tend to result in drift in position over time.
[0062] FIG. 4 illustrates, in cross-section, an embodiment of a
projection 50a and an associated electrostatic actuator 70. The
projection 50a includes a sub-projection 52. The sub-projection 52
is formed at the free end of the projection 50a from the main body
22. The sub-projection 52 may be formed or may have a top surface
of a high wear resistant material. It is the top surface of the
sub-projection 52 which forms part of the support surface 20.
[0063] The projection 50a may project from the top surface 25 of
the main body 22 in the direction of the optical axis and/or a
direction orthogonal to the top surface 25 of the main body 22 by a
few .mu.m. A cross-sectional area, in plan, of the sub-projection
52 is less than that of the projection 50a.
[0064] In an embodiment a stroke of the electrostatic actuator 70
is of the order of 100 nm, for example between 50 and 200 nm,
desirably between 80 and 120 nm.
[0065] The electrostatic actuator 70 displaces the free end of its
associated projection 50a (the surface of the sub-projection 52
distal from the top surface 25 of the main body 22) which forms the
support surface 20 relative to the main body 22. In an embodiment
such displacement is in a direction which at least includes a
component in the Z-direction. In another embodiment, for example as
described with reference to FIGS. 6-8, the projection 50a is
additionally or alternatively displaced in one or more directions
in the plane of the top surface 25 of the main body 22. In an
embodiment, the displacement is in one or more directions
orthogonal to the optical axis of the apparatus.
[0066] In an embodiment each electrostatic actuator 70 comprises
first and second electrically conductive layers 72, 74 as
electrodes. The electrically conductive layers 72, 74 are
electrically isolated from one another. In an embodiment the first
and second electrically conductive layers 72, 74 are in different
planes from one another. As illustrated in FIG. 4 the first and
second electrically conductive layers 72, 74 are in parallel planes
and separated from one another in the Z-direction. That is, the
first and second electrically conductive layers 72, 74 are
separated from one another in a direction perpendicular to the top
surface 25 of the main body 22 from which the projection 50a
projects.
[0067] The electrically conductive layers 72, 74 which are in a
plane parallel to the top surface of the main body 22 are easy to
manufacture. The layers may be deposited as layers onto the top
surface 25 using normal manufacturing techniques such as selective
laser sinter processes, spray/spin coating, sputtering, dry or wet
etching, PVD, CVD etc.
[0068] A gap 76 is present between the first electrically
conductive layer 72 and second electrically conductive layer 74.
The gap 76 may be a void. That is, the gap 76 may not be filled
with any material. The void may be a vacuum or a space at least
partly filled with gas. In an alternative embodiment the gap 76 may
be filled with a dielectric material. Preferably the dielectric
material has a low E modulus and is electrically insulating and
does not break down at the sort of charges generated between the
first and second electrically conductive layers 72, 74 (perhaps up
to 3000 V). The dielectric material in the gap 76 may be selected
from one or more materials in the group comprising: a glass, a
ceramic, a glass ceramic etc. The dielectric material may be
deposited using normal manufacturing techniques such as selective
laser sinter processes, spray/spin coating, sputtering, dry or wet
etching, PVD, CVD etc.
[0069] The gap 76 is typically a few .mu.m thick (say between 1 and
5 .mu.m thick).
[0070] In use the first and second electrically conductive layers
72, 74 have different charges applied to them. This results in
attraction or repulsion between the first and second electrically
conductive layers 72, 74 and corresponding movement towards or away
from each other. Thereby displacement of the free end of the
associated projection 50a relative to the main body, in the
Z-direction is achieved.
[0071] In use it is desirable to make the top electrode (in the
case of FIG. 4 of the second electrode 74) the ground electrode.
This prevents any charge applied to the electrically conductive
layers 72, 74 from reaching the substrate W. It may be enough to
ensure that the top electrically conductive layer of the
electrostatic actuator 70 is the one connected to ground in order
to ensure that electric fields associated with the electrostatic
actuator 70 to not interfere with the substrate W. A disadvantage
of electric fields associated with the electrostatic actuator 70
interfering with the substrate W is that it may be then harder to
remove the substrate W from the support 1 after imaging because an
attractive force may remain.
[0072] Alternatively or additionally an isolating electrically
conductive layer 90 is formed on the support 1 or in the substrate
support 1 above the electrostatic actuator 70. This shields the
substrate W from any electrostatic field generated by the
electrostatic actuator 70 by being connected to ground. In an
embodiment an isolating electrically conductive layer 95 may be
provided on the bottom side of the support 1 to isolate any
components under the substrate support 1 from fields associated
with the electrostatic actuators 70. One or more isolating
electrically conductive layers 90, 95 may be present in any
embodiment.
[0073] By measuring the flatness of the top surface of the
substrate W and adjusting the charge applied to the electrostatic
actuators 70, the flatness of the substrate W can be improved. A
control program for performing this task will be described below
with reference to FIG. 9.
[0074] FIG. 5 illustrates another embodiment of electrostatic
actuator 70. The embodiment of FIG. 5 is the same as that of FIG. 4
except as described below. The electrostatic actuator 70 of FIG. 5
comprises at least one further electrically conductive layer 82,
84, 86.
[0075] The advantage of providing multiple electrically conductive
layers 72, 74, 82, 84, 86 is that a greater stroke of the
electrostatic actuator 70 is possible. The electrostatic actuator
70 may have any number of electrically conductive layers 72, 74,
82, 84 associated with it.
[0076] In the embodiment of FIG. 5 each of the electrically
conductive layers 72, 74, 82, 84, 86 belongs to one of two groups.
Each of the electrically conductive layers 72, 84; 74, 82, 86 in a
group are connected together. For example, first electrically
conductive layer 72 and further electrically conductive layer 84
are connected together and second electrically conductive layer 74
is connected to further electrically conductive layers 82 and 86. A
charge can then be applied to all electrically conductive layers in
each group. In the embodiment of FIG. 5 the electrically conductive
layers 72, 74, 82, 84, 86 are split into two groups but the
electrically conductive layers 72, 74, 82, 84, 86 may be split into
any number of groups.
[0077] In an embodiment the electrically conductive layers 72, 74,
82, 84, 86 are not necessarily connected to any other electrically
conductive layer 72, 74, 82, 84, 86 and the charge to each
electrically conductive layer 72, 74, 82, 84, 86 or group may be
individually controlled.
[0078] FIG. 6 is an embodiment in which the free end of the
projection 50a is displaceable in a direction with a component in a
plane parallel to the surface of the main body 22 from which the
projection 50a projects. In the example of FIG. 6 the free end of
the projection 50a is displaceable in the Z-direction as well as
the X and Y-directions. In the embodiment of FIGS. 6 and 7 this is
achieved by use of three electrostatic actuators 70a, 70b, 70c
associated with the projection 50a. However, it may be possible to
design a single electrostatic actuator which can move the free end
of the projection 50a in the required directions, particularly if
this is only two of the Z, X and Y-directions. In an embodiment two
or more electrostatic actuators 70 may be associated with each
projection 50. With two electrostatic actuators it is possible to
arrange for movement in the Z-direction and in a direction
orthogonal to the Z-direction, for example.
[0079] In an embodiment the projection 50a is displaceable in one
or more of the X, Y, Z, Rx and Ry directions and in any combination
of those directions.
[0080] In the embodiment of FIG. 6 three electrostatic actuators
70a, 70b, 70c are used (most clearly seen in FIG. 7 which is a
cross-sectional view through line VII-VII in FIG. 6). However, a
different number of actuators may be used. Each of the three
associated electrostatic actuators 70a, 70b, 70c are the same as
the actuator 70 of the FIG. 5 embodiment. However, other
configurations are possible.
[0081] The associated electrostatic actuators 70a, 70b, 70c are
distributed around an axis 57 of the projection 50a. The actuators
70a, 70b, 70c are distributed evenly around the axis 57 of the
projection 70. The axis 57 of the projection 70 is in the
Z-direction. The projection 50a is, in plan, circular. The
actuators 70a, 70b, 70c have centers which are radially separated,
in plan, by substantially 120.degree., as seen in FIG. 7.
[0082] In the embodiment of FIGS. 6 and 7, by actuating the three
electrostatic actuators 70a, 70b, 70c movement of the free end of
the projection 50a both in the Z-direction and in the X and/or
Y-direction is possible. This is advantageous because it allows,
for example stress relief in the substrate W by moving the free end
of a projection in the X and/or Y-direction after the substrate W
has been clamped to the support 1.
[0083] The embodiment of FIGS. 6 and 7 is advantageous over other
ways of providing for movement of the projection 50a in the X and
Y-direction because the electrically conductive layers of each of
the electrostatic actuators 70a, 70b, 70c are in planes parallel to
the top surface 25 of the main body 22. Thus, normal techniques can
easily be used to deposit these layers.
[0084] The embodiment of FIGS. 6 and 7 have electrostatic actuators
70a, 70b, 70c which are circular in plan. However, this need not be
the case. FIG. 8 illustrates an embodiment which is the same as
that of FIG. 7 except that the shape in plan of the electrostatic
actuators 70a, 70b, 70c different.
[0085] In the embodiment of FIG. 8, in order to maximize the
surface area of the electrostatic actuators 70a, 70b, 70c (and
thereby their achievable force), the shape of the electrostatic
actuators has been made a wedge shape. This maximizes the surface
area of the electrically conductive layers of each electrostatic
actuator 70a, 70b, 70c for a given total footprint of the
electrostatic actuators 70a, 70b, 70c.
[0086] The support 1 may form part of a substrate table WT. Such a
substrate table WT may be used in a lithographic apparatus, for
example a projection lithographic apparatus.
[0087] A controller 500 is provided. The controller 500 is adapted
to apply a charge to each electrostatic actuator 70. In an
embodiment a part of the controller 500', 500'' may be provided on
the support 1, as for example illustrated in FIG. 9. However, this
is not necessarily the case and the controller 500 may be provided
elsewhere and may be a controller which controls other parts of the
lithographic apparatus. The controller 500 is adapted individually
to address each projection 50.
[0088] FIG. 9 illustrates a control system for interconnecting
electrostatic actuators 70. One of the electrically conductive
layers of each electrostatic actuator 70 may be connected to
another electrically conductive layer of another electrostatic
layer to form a grid such as illustrated in FIG. 9. Each
electrically conductive layer is connected to the controller 500
using a crossed electrical network. This allows each electrostatic
actuator 70 to be individually addressable. For example, in order
to address one electrically conductive layer of the bottom right
hand electrostatic actuator 70d illustrated in FIG. 9, the
controller 500'' at the top addresses the right hand most line and
the controller 500' at the right addresses the bottom most line. A
second crossed electrical network the same as that illustrated in
FIG. 9 may be provided for the other of the electrically conductive
layers of the electrostatic actuators 70. In this way it is
possible individually to address each of the layers of a specific
electrostatic actuator, e.g., 70d, and apply a charge.
[0089] Once a connection with the electrostatic actuator 70 has
been broken, that charge remains on the electrostatic actuator (to
be more specific, the charge remains between electrically
conductive layers of the electrostatic actuator 70). Because of the
nature of electrostatic actuators 70 mentioned above (their
stability over time) once the charge of the electrostatic actuator
70 has been set, the displacement of the electrostatic actuator 70
will not vary appreciably. Therefore, it is possible using a
crossed electrical network as described above individually to
address the 40,000 to 60,000 projections on a typical support 1 in
a relatively short time (crossed electrical networks can operate at
100 MHz allowing 100,000,000 projections a second to be
addressed).
[0090] A control method will now be described. A level sensor 600
is used to measure the flatness of the top surface of a substrate
W. Based on the results of the level sensor 600, a charge may be
applied to one or more electrostatic actuators 70 associated with a
projection 50 at which position an unflatness has been detected.
After an adjustment has been made to one or more electrostatic
actuators 70, the level sensor 600 may be used again to measure the
flatness of the top surface of the substrate W. If the flatness
does not fall within a certain tolerance, for example a
pre-determined tolerance, the position of one or more of the
electrostatic actuators 70 may (again or for the first time) be
varied. This loop can be continued until the measurement step
indicates that the flatness of the substrate W falls within the
certain tolerance.
[0091] If the top most electrically conductive layer 74 of the
electrostatic actuator 70 is not pre-determined to be ground (for
example because of the use or an isolating electrically conductive
layer 90 as described above) then adjustment of the electrostatic
actuators 70 may start at zero charge being applied to the
electrostatic actuators 70. This is because displacement in both
towards and away from the top surface 25 of the main body 22 may be
implemented (in the Z-direction). Therefore, it is possible to
apply either a positive or negative charge to the top electrically
conductive layer 74 as this will not effect the substrate W.
However, if the top most electrically conductive layer 74 must be
the one connected to ground in order to avoid electrical fields
associated with the electrostatic actuator 70 from interfering with
the substrate W, it may be desirable before the first flatness
measurement is made to supply each of the actuators with a charge
equal to 50% of the maximum charge. In this way it is possible to
actuate the electrostatic actuators 70 in both positively and
negatively in the Z-direction, whichever is required.
[0092] The controller 500 is adapted to control the magnitude of
charge applied to each electrostatic actuator 70. In this way the
controller 500 applies the electrostatic charge to each
electrostatic actuator based on an input signal from the level
sensor 600. In subsequent adjustment steps the charge applied to
one or more electrostatic actuators 70 may be varied. Alternatively
or additionally in subsequent steps through the loop charges may be
applied to electrostatic actuators 70 which did not initially have
a charge applied.
[0093] This system may not eliminate all unflatness of a substrate
W but can reduce it to within an acceptable level. Any support 1
deformations induced due to motion of the support 1 are small
compared to the unflatness of the substrate W. Additionally such
deformations are predictable and so can be compensated for by, for
example, movement of the support 1 during imaging.
[0094] The system may be used to achieve an approximation to local
flatness. For example it may be undesirable to attempt to remove
any global unflatness because a substrate support 1 may in any case
be relatively flexible and will bend due to acceleration forces
unavoidably. Therefore, the system of the present invention may be
used to achieve an approximation to local flatness rather than an
approximation to global flatness.
[0095] The main body 22 of the substrate support 1 may be based on
a SiSiC material which has been found to be suitable for achieving
good flatness. However, because of the provision of electrostatic
actuators 70 associated with each projection 50, flatness of the
main body 22 is not so critical. Therefore, other materials could
alternatively be used for the main body 22.
[0096] Wires interconnecting the electrically conducting layers of
the electrostatic actuators to the controller 500 may pass through
an underside of the main body 22 of the substrate support 1, for
example.
[0097] Although specific reference may be made in this text to the
use of lithographic apparatus in the manufacture of ICs, it should
be understood that the lithographic apparatus described herein may
have other applications, such as the manufacture of integrated
optical systems, guidance and detection patterns for magnetic
domain memories, flat-panel displays, liquid-crystal displays
(LCDs), thin-film magnetic heads, etc. The skilled artisan will
appreciate that, in the context of such alternative applications,
any use of the terms "wafer" or "die" herein may be considered as
synonymous with the more general terms "substrate" or "target
portion", respectively. The substrate referred to herein may be
processed, before or after exposure, in for example a track (a tool
that typically applies a layer of resist to a substrate and
develops the exposed resist), a metrology tool and/or an inspection
tool. Where applicable, the disclosure herein may be applied to
such and other substrate processing tools. Further, the substrate
may be processed more than once, for example in order to create a
multi-layer IC, so that the term substrate used herein may also
refer to a substrate that already contains one or multiple
processed layers.
[0098] Although specific reference may have been made above to the
use of embodiments of the invention in the context of optical
lithography, it will be appreciated that the invention may be used
in other applications, for example imprint lithography, and where
the context allows, is not limited to optical lithography. In
imprint lithography a topography in a patterning device defines the
pattern created on a substrate. The topography of the patterning
device may be pressed into a layer of resist supplied to the
substrate whereupon the resist is cured by applying electromagnetic
radiation, heat, pressure or a combination thereof. The patterning
device is moved out of the resist leaving a pattern in it after the
resist is cured.
[0099] The terms "radiation" and "beam" used herein encompass all
types of electromagnetic radiation, including ultraviolet (UV)
radiation (e.g., having a wavelength of or about 436, 405, 365,
355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV)
radiation (e.g., having a wavelength in the range of 5-20 nm), as
well as particle beams, such as ion beams or electron beams.
[0100] While specific embodiments of the invention have been
described above, it will be appreciated that the invention may be
practiced otherwise than as described. For example, the embodiments
of the invention may take the form of a computer program containing
one or more sequences of machine-readable instructions describing a
method as disclosed above, or a data storage medium (e.g.,
semiconductor memory, magnetic or optical disk) having such a
computer program stored therein. Further, the machine readable
instruction may be embodied in two or more computer programs. The
two or more computer programs may be stored on one or more
different memories and/or data storage media.
[0101] The invention may be applied to substrates with a diameter
of 300 mm or 450 mm or any other size.
[0102] Any controllers described herein may each or in combination
be operable when the one or more computer programs are read by one
or more computer processors located within at least one component
of the lithographic apparatus. The controllers may each or in
combination have any suitable configuration for receiving,
processing, and sending signals. One or more processors are
configured to communicate with the at least one of the controllers.
For example, each controller may include one or more processors for
executing the computer programs that include machine-readable
instructions for the methods described above. The controllers may
include a data storage medium or data storage media for storing
such computer programs, and/or hardware to receive such a
medium/media. So the controller(s) may operate according the
machine readable instructions of one or more computer programs.
[0103] One or more embodiments of the invention may be applied to
any immersion lithography apparatus, whether the immersion liquid
is provided in the form of a bath, only on a localized surface area
of the substrate, or is unconfined. In an unconfined arrangement,
the immersion liquid may flow over the surface of the substrate
and/or substrate table so that substantially the entire uncovered
surface of the substrate table and/or substrate is wetted. In such
an unconfined immersion system, the liquid supply system may not
confine the immersion liquid or it may provide a proportion of
immersion liquid confinement, but not substantially complete
confinement of the immersion liquid.
[0104] In an embodiment, the lithographic apparatus is a
multi-stage apparatus comprising two or more tables located at the
exposure side of the projection system, each table comprising
and/or holding one or more objects. In an embodiment, one or more
of the tables may hold a radiation-sensitive substrate. In an
embodiment, one or more of the tables may hold a sensor to measure
radiation from the projection system. In an embodiment, the
multi-stage apparatus comprises a first table configured to hold a
radiation-sensitive substrate (i.e., a substrate table) and a
second table not configured to hold a radiation-sensitive substrate
(referred to hereinafter generally, and without limitation, as a
measurement and/or cleaning table). The second table may comprise
and/or may hold one or more objects, other than a
radiation-sensitive substrate. Such one or more objects may include
one or more selected from the following: a sensor to measure
radiation from the projection system, one or more alignment marks,
and/or a cleaning device (to clean, e.g., the liquid confinement
structure).
[0105] In an embodiment, the lithographic apparatus may comprise an
encoder system to measure the position, velocity, etc. of a
component of the apparatus. In an embodiment, the component
comprises a substrate table. In an embodiment, the component
comprises a measurement and/or cleaning table. The encoder system
may be in addition to or an alternative to the interferometer
system described herein for the tables. The encoder system
comprises a sensor, transducer or readhead associated, e.g.,
paired, with a scale or grid. In an embodiment, the movable
component (e.g., the substrate table and/or the measurement and/or
cleaning table) has one or more scales or grids and a frame of the
lithographic apparatus with respect to which the component moves
has one or more of sensors, transducers or readheads. The one or
more of sensors, transducers or readheads cooperate with the
scale(s) or grid(s) to determine the position, velocity, etc. of
the component. In an embodiment, a frame of the lithographic
apparatus with respect to which a component moves has one or more
scales or grids and the movable component (e.g., the substrate
table and/or the measurement and/or cleaning table) has one or more
of sensors, transducers or readheads that cooperate with the
scale(s) or grid(s) to determine the position, velocity, etc. of
the component.
[0106] The term "lens", where the context allows, may refer to any
one or combination of various types of optical components,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical components.
[0107] The descriptions above are intended to be illustrative, not
limiting. Thus, it will be apparent to one skilled in the art that
modifications may be made to the invention as described without
departing from the scope of the claims set out below.
[0108] It is to be appreciated that the Detailed Description
section, and not the Summary and Abstract sections, is intended to
be used to interpret the claims. The Summary and Abstract sections
may set forth one or more but not all exemplary embodiments of the
present invention as contemplated by the inventor(s), and thus, are
not intended to limit the present invention and the appended claims
in any way.
[0109] The present invention has been described above with the aid
of functional building blocks illustrating the implementation of
specified functions and relationships thereof. The boundaries of
these functional building blocks have been arbitrarily defined
herein for the convenience of the description. Alternate boundaries
can be defined so long as the specified functions and relationships
thereof are appropriately performed.
[0110] The foregoing description of the specific embodiments will
so fully reveal the general nature of the invention that others
can, by applying knowledge within the skill of the art, readily
modify and/or adapt for various applications such specific
embodiments, without undue experimentation, without departing from
the general concept of the present invention. Therefore, such
adaptations and modifications are intended to be within the meaning
and range of equivalents of the disclosed embodiments, based on the
teaching and guidance presented herein. It is to be understood that
the phraseology or terminology herein is for the purpose of
description and not of limitation, such that the terminology or
phraseology of the present specification is to be interpreted by
the skilled artisan in light of the teachings and guidance.
[0111] The breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *